1. Field of the Invention
This invention relates to a rotation state detecting device and a rotation state detecting method for detecting the rotation state of a pronged magnetic rotating body.
2. Description of the Related Art
Generally, for example in an engine of an automotive vehicle, to detect the speed of the engine and the ignition timing of multiple cylinders, a revolution sensor is provided. In a revolution sensor, for example as shown in JP-A-2000-337922, ‘Rotation Detecting Device’, a magnet for directing a bias field at the teeth of a rotating toothed wheel and two magneto-resistance effect element patterns whose resistance values change along with changes in the bias field are provided, the two magneto-resistance effect element patterns are disposed symmetrically about the magnetic center axis of the bias magnet, and changes in the magnetic field caused by rotation of the toothed wheel are outputted as voltages. By the difference between the outputs of the two magneto-resistance effect element patterns being taken, it is intended that offset caused by manufacturing factors and power source fluctuations and noise and the like are canceled out and the rotation is detected accurately.
And in JP-A-2001-108700, ‘Rotating Body Reverse Rotation Detecting Device and Reverse Rotation Detecting Method’, one pair of magneto-resistance effect element patterns is provided and reverse rotation is detected by an analog threshold level being set.
In a rotation detecting device of the kind shown in JP-A-2000-337922, a speed of rotation is detected by taking the difference between the outputs of two magneto-resistance effect element patterns, and there has been the problem that even if the toothed wheel rotates backward, the output waveform is the same (FIG. 2 of JP-A-2000-337922), and consequently the rotation direction of the toothed wheel cannot be detected. In present engines, when the engine has stopped in the fuel compression stroke, the reaction of the compressed air sometimes causes the crankshaft to rotate backward. With rotation detecting devices of related art, because the rotation direction cannot be detected, even if this kind of backward rotation occurs, the problem may arise that this is detected as forward rotation and consequently the ignition timing of the cylinders is wrong the next time the engine is started.
And in a reverse rotation detecting device according to JP-A-2001-108700, ‘Rotating Body Reverse Rotation Detecting Device and Reverse Rotation Detecting Method’, it is necessary to set two threshold levels from outside, and there has been the problem that due to dispersion among devices and mounting accuracy issues it has been necessary to adjust each device individually.